Pension and Other Retirement Benefits - Components of Net Periodic Benefit Expense Related to Post-Retirement Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net periodic expense
Interest cost	$ 5	$ 5
Pension Plans
Components of net periodic expense
Service cost	5	4
Interest cost	4	5
Expected return on plan assets	(5)	(5)
Amortization of net actuarial loss from earlier periods	2	1
Amortization of net prior service costs from earlier periods	0	0
Net periodic expense	6	5
Other Retirement Plans
Components of net periodic expense
Service cost	1	1
Interest cost	0	0
Expected return on plan assets	0	0
Amortization of net actuarial loss from earlier periods	0	0
Amortization of net prior service costs from earlier periods	0	0
Net periodic expense	$ 1	$ 1